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Research Papers: Multiphase Flows

Measurements of High Velocity Gradient Flow Using Bubble Tracers in a Cavitation Tunnel

[+] Author and Article Information
Bu-Geun Paik

Maritime and Ocean Engineering Research Institute, KORDI, Jang-dong 171, Yuseong-gu, Daejeon 305-343, Koreappaik@moeri.re.kr

Kyung-Youl Kim, Jong-Woo Ahn

Maritime and Ocean Engineering Research Institute, KORDI, Jang-dong 171, Yuseong-gu, Daejeon 305-343, Korea

J. Fluids Eng 131(9), 091301 (Aug 12, 2009) (10 pages) doi:10.1115/1.3192136 History: Received September 03, 2008; Revised June 23, 2009; Published August 12, 2009

The objective of the present study is to investigate propeller wake using particle image velocimetry (PIV) technique with bubble type of tracers, naturally generated by the decrease in the static pressure in a cavitation tunnel. The bubble can be grown from the nuclei melted in the water tunnel and the size of bubbles is changed by varying the tunnel pressure. A series of experiments are conducted in the conditions of the uniform and high velocity gradient flows to find out the characteristics of bubble tracers and compared the measurement results using bubbles with those using solid particles. Bubbles showed good trace ability in the region of 15<ReS<75; however, some discrepancies showed at high velocity gradient region of ReS1000. The fitted vorticity reduction rate would give reference for the prediction in a real flow when bubble tracers are utilized in PIV measurements of a vortical flow. In addition, the characteristics of bubble slip velocity can provide information on the vortex core center and the reduction in the Reynolds shear stress caused by bubble’s deformability.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of a cavitation tunnel

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Figure 2

Schematic diagram of a PIV experimental setup

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Figure 3

One image of shadowgraph technique at 0.38 atm

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Figure 4

Particle images at the tunnel pressure of 0.2 atm: (a) 3 m/s, (b) 5 m/s, and (c) 8 m/s

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Figure 5

Velocity fields at the tunnel pressure of 0.2 atm: (a) 3 m/s, (b) 5 m/s, and (c) 8 m/s

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Figure 6

Particle images of propeller wake at the same free stream velocity: (a) atmospheric pressure and (b) 0.25 atm

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Figure 7

Instantaneous fluctuating velocity fields subtracted by a convection velocity at the same free stream velocity: (a) atmospheric pressure and (b) 0.25 atm

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Figure 8

The comparison of the phase-averaged axial velocity contours: (a) solid particles and (b) bubble tracers

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Figure 9

The comparison of the phase-averaged axial velocity profiles at several radial locations

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Figure 10

Contour plots of slip velocity between bubble and solid tracers: (a) for velocity magnitude and (b) for vertical velocity

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Figure 11

The comparison of the phase-averaged vorticity contours: (a) solid particles and (b) bubble tracers

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Figure 12

The comparison of the phase-averaged vorticity profiles at several radial locations

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Figure 13

The comparison of the vorticity values at the cores of tip vortices

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Figure 14

The comparison of the Reynolds shear stress profiles at several radial locations

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